Anesthesiologists commonly use nerve stimulators and insulated needles for the purpose of locating peripheral nerves, or nerve plexuses, for the performance of regional anesthesia procedures. This procedure is discussed in Vloka J D et al., “A National Survey On Practice Patterns In The Use Of Peripheral Nerve Stimulators In Regional Anesthesia,” The Internet Journal of Anesthesiology, Vol. 3, No. 4, 1999. In addition to targeting local anesthetic delivery for regional anesthesia, the use of nerve stimulators reduces the potential for nerve injury since direct contact with the nerve is not required for performance of the anesthetic. This is in contrast to the alternative method of seeking paresthesias to confirm needle position. Paresthesias are provoked by directly disturbing the nerve. If such needle to nerve contact can be avoided, direct needle trauma should be reduced.
The available nerve stimulators have differing output characteristics. The shape of the pulse is typically square or nearly so. The pulse widths vary from 40 microseconds (μs) to 2 milliseconds (ms). Frequency selections for these stimulators range from 1.0 Hertz (Hz) to 100 Hz, in step gradations rather than continuously. Stimulators that are manufactured specifically for regional anesthesia applications typically do not have frequency options greater than 5 Hz. The stimulators that serve as both nerve stimulators and neuromuscular blockade monitors offer higher frequency choices, typically 50 and 100 Hz. These stimulators are discussed in Barthram C N, “Nerve Stimulators For Nerve Location—Are They All The Same?,” Anaesthesia, Vol. 52, 1997, pp. 761–764.
The needles used for stimulator assisted regional anesthesia typically have a molded plastic hub that contains both a connection to plastic tubing and a wire attached to the metal needle imbedded in the hub. This wire, when connected to a source, supplies electrical current to the needle with appropriate output characteristics for generation of action potentials in axons. Use of this equipment requires a means for holding the needle assembly, adjusting the output current, and injecting medication. This is awkward for a single user to accomplish and usually requires the presence of an assistant.
The commercially available nerve stimulators offer two methods of controlling the current output from the nerve stimulator instrument to a nerve stimulator needle. The first method is by hand-operated dials on the face of the nerve stimulator instruments. In this method, it is difficult for a single operator to insert and position the needle in the patient, control the current supplied the nerve stimulator needle, and inject the medication in the patient.
The second method is by a foot-operated pedal connected via a cable to the nerve stimulator instrument. An output source with foot-pedal control, such as described in U.S. Pat. No. 5,830,151 to Hadzic, necessitates a multiplicity of wires connecting pieces of equipment together. In the environment of an operating room where a multiplicity of electrical cables already exists, any equipment that adds additional cables spread out across the floor or tables and carts represents increased hazard for stumbling and consequent injury. Also, efficiency of movement is highly prized in the operating room environment. When an anesthetic procedure is completed, the operating room personnel move rapidly to begin the surgical positioning and prepping. Often, the anesthesiologist is in the position of gathering up equipment used for a procedure, and either disposing of it or placing it on a cart for subsequent storage. Tangles of cables and wires complicate this process and have a tendency to increase the clutter surrounding anesthesia machines and carts.
U.S. Pat. No. 4,515,168 to Chester et al. discloses to clamp a nerve stimulator and locating device onto a syringe. As the entire nerve stimulator device is clamped onto the syringe, the unit is a long and clumsy assembly, which is difficult to maneuver. Moreover, the device disclosed by Chester does not allow for one-handed operation of needle advancement and current control. Particularly, the needle is advanced by one hand while the current must be controlled by turning the knob 27 with the other hand, which is an extremely awkward operation for the user. Additionally, the nerve stimulator of the Chester patent restricts the size of the syringe upon which it may be mounted, thus, requiring the operator to change the syringe on the needle. This combination makes it very difficult to stabilize the needle within 1–2 mm of a nerve as desired for a regional block.
U.S. Pat. No. 5,306,236 to Blumenfeld et al. discloses a handle 36 to which the syringe, the needle and a conductor for carrying an electrical signal are attached. The control mechanism for controlling the application of current to the needle is located remotely from the needle at a stimulator device. Like the Chester patent, the system of Blumenfeld also does not allow for one-handed operation of both needle advancement and current control. Accordingly, the system of the Blumenfeld patent also provides a clumsy operation for the user.
It is frequently useful, during and after the performance of a regional anesthetic procedure, to know the depth at which the nerve structure was located. The consideration of needle tip depth is valuable both for medical record purposes as well as a check on needle position during the performance of a procedure. Accurate initial needle position may be obtained, but then undergo alteration by displacement during the injection portion of the procedure. Displacement may be due to inadvertent pressure applied by the operator, or the tendency of the injected fluid to force the needle back along its tissue track. The presence of visual guides on the needle itself, or a read out of needle tip depth on the nerve stimulator device, would provide feedback to the operator so as to prevent needle displacement. At present, there is no mechanism for providing such information with the currently available needles designed for use with nerve stimulators.